More detailed backtrace:

# apport-retrace /var/crash/_usr_sbin_apache2.0.crash  --stdout -S system
Installing extra package apache2-bin to get ExecutablePath
dpkg-source: info: extracting apache2 in apache2-2.4.33
dpkg-source: info: unpacking apache2_2.4.33.orig.tar.bz2
dpkg-source: info: unpacking apache2_2.4.33-3ubuntu2.debian.tar.xz
dpkg-source: info: applying fhs_compliance.patch
dpkg-source: info: applying no_LD_LIBRARY_PATH.patch
dpkg-source: info: applying suexec-CVE-2007-1742.patch
dpkg-source: info: applying customize_apxs.patch
dpkg-source: info: applying build_suexec-custom.patch
dpkg-source: info: applying reproducible_builds.diff
dpkg-source: info: applying mod_http2_mem_usage_32bit.diff
dpkg-source: info: applying 086_svn_cross_compiles
W: Download is performed unsandboxed as root as file 'apache2_2.4.33-3ubuntu2.dsc' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
--- stack trace ---
#0  impl_pollset_remove (pollset=0x7feae06aa050, descriptor=0x0) at ./poll/unix/epoll.c:224
        ep = <optimized out>
        rv = 0
        ev = {events = 32766, data = {ptr = 0x56391f4e16a0, fd = 525211296, u32 = 525211296, u64 = 94803338335904}}
        ret = <optimized out>
#1  0x00007feadcf8cbe2 in disable_listensocks () at event.c:470
        i = 0
        i = <optimized out>
#2  0x00007feadcf8cc33 in wakeup_listener () at event.c:578
No locals.
#3  0x00007feadcf8cd74 in signal_threads (mode=1) at event.c:627
No locals.
#4  0x00007feadcf8a94a in child_main (child_num_arg=child_num_arg@entry=0, child_bucket=child_bucket@entry=0) at event.c:2579
        threads = 0x56391f4e16a0
        rv = 2
        ts = 0x7feae06a9af8
        thread_attr = 0x7feae06a9b18
        start_thread_id = 0x7feae06a9b78
        i = <optimized out>
#5  0x00007feadcf8d05a in make_child (s=0x7feae07414a0, slot=slot@entry=0, bucket=0) at event.c:2663
        pid = 0
#6  0x00007feadcf8dedd in server_main_loop (num_buckets=1, remaining_children_to_start=2) at event.c:2933
        ps = <optimized out>
        status = 0
        pid = {pid = 26968, in = 0x7feadfe8dcd6 <find_entry+134>, out = 0x0, err = 0x9}
        i = <optimized out>
        child_slot = 0
        exitwhy = APR_PROC_EXIT
        processed_status = 0
        child_slot = <optimized out>
        exitwhy = <optimized out>
        status = <optimized out>
        processed_status = <optimized out>
        pid = <optimized out>
        i = <optimized out>
        sr__ = <optimized out>
        ps = <optimized out>
        sr__ = <optimized out>
#7  event_run (_pconf=<optimized out>, plog=<optimized out>, s=<optimized out>) at event.c:3051
        num_buckets = 1
        remaining_children_to_start = <optimized out>
        i = <optimized out>
#8  0x000056391d475b7e in ap_run_mpm (pconf=0x7feae076c028, plog=0x7feae073a028, s=0x7feae07414a0) at mpm_common.c:94
        pHook = <optimized out>
        n = 0
        rv = -1
#9  0x000056391d46e46b in main (argc=<optimized out>, argv=<optimized out>) at main.c:818
        c = 0 '\000'
        showcompile = 0
        showdirectives = 0
        confname = 0x56391d4b57e5 "apache2.conf"
        def_server_root = 0x56391d4b57d8 "/etc/apache2"
        temp_error_log = <optimized out>
        error = <optimized out>
        process = <optimized out>
        pconf = 0x7feae076c028
        plog = 0x7feae073a028
        ptemp = 0x7feae0730028
        pcommands = 0x7feae0744028
        opt = 0x7feae0744118
        rv = <optimized out>
        mod = <optimized out>
        opt_arg = 0x7feae076e028 "( w\340\352\177"
        signal_server = <optimized out>
        rc = <optimized out>
--- source code stack trace ---
#0  impl_pollset_remove (pollset=0x7feae06aa050, descriptor=0x0) at ./poll/unix/epoll.c:224
  [Error: epoll.c was not found in source tree]
#1  0x00007feadcf8cbe2 in disable_listensocks () at event.c:470
  465:     if (apr_atomic_cas32(&listensocks_disabled, 1, 0) != 0) {
  466:         return;
  467:     }
  468:     if (event_pollset) {
  469:         for (i = 0; i < num_listensocks; i++) {
  470:             apr_pollset_remove(event_pollset, &listener_pollfd[i]);
  471:         }
  472:     }
  473:     ap_scoreboard_image->parent[ap_child_slot].not_accepting = 1;
  474: }
  475: 
#2  0x00007feadcf8cc33 in wakeup_listener () at event.c:578
  573: }
  574: 
  575: static void wakeup_listener(void)
  576: {
  577:     listener_may_exit = 1;
  578:     disable_listensocks();
  579: 
  580:     /* Unblock the listener if it's poll()ing */
  581:     if (event_pollset && listener_is_wakeable) {
  582:         apr_pollset_wakeup(event_pollset);
  583:     }
#3  0x00007feadcf8cd74 in signal_threads (mode=1) at event.c:627
  622:     retained->mpm->mpm_state = AP_MPMQ_STOPPING;
  623: 
  624:     /* in case we weren't called from the listener thread, wake up the
  625:      * listener thread
  626:      */
  627:     wakeup_listener();
  628: 
  629:     /* for ungraceful termination, let the workers exit now;
  630:      * for graceful termination, the listener thread will notify the
  631:      * workers to exit once it has stopped accepting new connections
  632:      */
#4  0x00007feadcf8a94a in child_main (child_num_arg=child_num_arg@entry=0, child_bucket=child_bucket@entry=0) at event.c:2579
  2574:             if (rv == AP_MPM_PODX_GRACEFUL || rv == AP_MPM_PODX_RESTART) {
  2575:                 /* make sure the start thread has finished;
  2576:                  * signal_threads() and join_workers depend on that
  2577:                  */
  2578:                 join_start_thread(start_thread_id);
  2579:                 signal_threads(rv ==
  2580:                                AP_MPM_PODX_GRACEFUL ? ST_GRACEFUL : ST_UNGRACEFUL);
  2581:                 break;
  2582:             }
  2583:         }
  2584: 
#5  0x00007feadcf8d05a in make_child (s=0x7feae07414a0, slot=slot@entry=0, bucket=0) at event.c:2663
  2658:                          "processor unbind failed");
  2659: #endif
  2660:         RAISE_SIGSTOP(MAKE_CHILD);
  2661: 
  2662:         apr_signal(SIGTERM, just_die);
  2663:         child_main(slot, bucket);
  2664:         /* NOTREACHED */
  2665:         ap_assert(0);
  2666:         return -1;
  2667:     }
  2668: 
#6  0x00007feadcf8dedd in server_main_loop (num_buckets=1, remaining_children_to_start=2) at event.c:2933
  2928:                 }
  2929:                 else if (remaining_children_to_start) {
  2930:                     /* we're still doing a 1-for-1 replacement of dead
  2931:                      * children with new children
  2932:                      */
  2933:                     make_child(ap_server_conf, child_slot, ps->bucket);
  2934:                     --remaining_children_to_start;
  2935:                 }
  2936:             }
  2937: #if APR_HAS_OTHER_CHILD
  2938:             else if (apr_proc_other_child_alert(&pid, APR_OC_REASON_DEATH,
#7  event_run (_pconf=<optimized out>, plog=<optimized out>, s=<optimized out>) at event.c:3051
  3046:     ap_log_command_line(plog, s);
  3047:     ap_log_mpm_common(s);
  3048: 
  3049:     retained->mpm->mpm_state = AP_MPMQ_RUNNING;
  3050: 
  3051:     server_main_loop(remaining_children_to_start, num_buckets);
  3052:     retained->mpm->mpm_state = AP_MPMQ_STOPPING;
  3053: 
  3054:     if (retained->mpm->shutdown_pending && retained->mpm->is_ungraceful) {
  3055:         /* Time to shut down:
  3056:          * Kill child processes, tell them to call child_exit, etc...
#8  0x000056391d475b7e in ap_run_mpm (pconf=0x7feae076c028, plog=0x7feae073a028, s=0x7feae07414a0) at mpm_common.c:94
  89: AP_IMPLEMENT_HOOK_RUN_ALL(int, monitor,
  90:                           (apr_pool_t *p, server_rec *s), (p, s), OK, DECLINED)
  91: AP_IMPLEMENT_HOOK_RUN_ALL(int, drop_privileges,
  92:                           (apr_pool_t * pchild, server_rec * s),
  93:                           (pchild, s), OK, DECLINED)
  94: AP_IMPLEMENT_HOOK_RUN_FIRST(int, mpm,
  95:                             (apr_pool_t *pconf, apr_pool_t *plog, server_rec *s),
  96:                             (pconf, plog, s), DECLINED)
  97: AP_IMPLEMENT_HOOK_RUN_FIRST(int, mpm_query,
  98:                             (int query_code, int *result, apr_status_t *_rv),
  99:                             (query_code, result, _rv), DECLINED)
#9  0x000056391d46e46b in main (argc=<optimized out>, argv=<optimized out>) at main.c:818
  813:         apr_pool_lock(pconf, 1);
  814: 
  815:         ap_run_optional_fn_retrieve();
  816: 
  817:         ap_main_state = AP_SQ_MS_RUN_MPM;
  818:         rc = ap_run_mpm(pconf, plog, ap_server_conf);
  819: 
  820:         apr_pool_lock(pconf, 0);
  821: 
  822:     } while (rc == OK);
  823: